Greenhouse disease update for Botrytis blight

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Stem, leaf, and flower blights caused by the fungus, Botrytis cinerea, can limit all phases of ornamental production. Botrytis is well known for its ability to produce large masses of gray conidia that may be picked up and carried on air currents and transported to healthy plants where blight can become established. Monitoring the occurrence and build-up of this inoculum in the greenhouse can signal the need for implementing control measures. On bedding and stock plants, Botrytis typically becomes established and produces spores on aging lower leaves that are near the moist soil surface and under the plant canopy. In addition, Botrytis readily infects the broken or cut stem surface of stock plants and progresses downward, causing a dieback of the entire stem.

Fungicides are often important in managing Botrytis and should be chosen carefully. Geraniums are good test plants because they seem to be a “magnet” for this disease .All fungicides are applied and allowed to dry prior to introducing Botrytis spores. Each time a test is conducted, fungicides that are considered especially effective are included for a comparison.Over the years of testing fungicides for Botrytis control, Decree, Chipco 26 GT, and fungicides containing chlorothalonil (Daconil and Echo) have been used as standards because they consistently provide effective control.

Evaluation of fungicides for control of Botrytis blight of poinsettia

Disease pressure was severe in this trial with the untreated plants receiving a rating of 8.3 (10 equals plant death) by the end of the trial. All treatments with the exception of Actinovate and Insignia significantly reduced infected leaves and disease severity by the final rating date.On December 18, plants treated with the experimental fungicide V-10135 had significantly fewer infected leaves and less overall disease severity than the untreated control and all other treatments except Decree 50WDG, Palladium 62.5WG (not yet registered), Veranda 11.3DF, and Chipco 26019 50WDG.Similar results were seen for number of leaves with pathogen sporulation.Spray residue was evaluated for all of the treatments. Of the products shown to be effective in this trial, those with the least residue included Palladium 62.5WG and Veranda 11.3DF.

Evaluation of registered and unregistered fungicides for control of Botrytis blight of geranium, 2009

Disease pressure was severe in this trial with the untreated inoculated plants averaging 26 leaves sporulating with B. cinerea on the final rating date. Although all treatments significantly reduced infection compared to the untreated control, statistical differences were observed among treatments. Unregistered fungicide Fluazinam completely prevented infection in this trial.Industry standard Daconil Weather Stick and unregistered product Palladium were very effective and limited infection to just 1.3 and 0.8 infected leaves per plant, respectively. A significant rate response was not observed with Disarm O or the biopesticide Veranda O treatments. Phytotoxicity in the form of chlorosis and necrotic leaf margins was observed on plants treated with Palladium WDG.

Botrytis on poinsettia
Botrytis on geranium
Fungicides to consider
The "B" Team


This research was funded in part by Floriculture Nursery and Research Initiative of the Agricultural Research Service under Cooperative Agreement #59-1907-5-553 and by the American Floral Endowment.


Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

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